The goal of this research project is to elucidate the role of the choroid plexuses and arachnoid membranes in a) the secretion of the cerebrospinal fluid (CSF), and b) the maintenance of the 'blood- cerebrospinal fluid barrier'. In vitro preparations of choroid plexuses and arachnoid membranes will be used to investigate 1) cellular and molecular mechanisms responsible for CSF secretion; 2) mechanisms of ion (e.g.K, H, I, Ca, and Mg) and non-electrolytes (e.g. amino acids, sugars, and metabolites) transport between CSF and blood; 3) the exchange of hallucinogenic drugs and narcotic analgesics between CSF and blood; 4) mechanisms of passive solute and water permeation; and 5) the role of cilia in i) bulk mixing of the CSF, and ii) the transport of solutes and water across these membranes. The methods to be used are largely those that have been used so successfully to study transport across other epithelial membranes such as the kidney, gall bladder and intestine. These included radioactive tracer techniques to measure unidirectional fluxes across the epithelium and across cell membranes, electrophysiological techniques to measure passive permeability characteristics of membranes, and fluorescence techniques to probe intracellular accumulation and metabolism in intact cells. The function of cilia will be studied by a combination of optical, electrical and tracer techniques. In vitro preparations of frog choroid plexuses and arachnoid membranes that have developed in this laboratory will be used in this investigation. Every endeavour will be made to extend the results of this project to the further understanding of the physiology and pathology of the CSF in higher vertebrates.